Paula Cleggett-Haleim
Headquarters, Washington, D.C. January 25, 1991
(Phone: 202/453-1547)
Robert McMillin
Jet Propulsion Laboratory, Pasadena, Calif.
(Phone: 818/354-5011)
RELEASE: 91-12
MAGELLAN MAPPING OF VENUS PROVIDES SIGNIFICANT NEW KNOWLEDGE
The Magellan spacecraft mapping the surface of Venus with imaging
radar has swept over nearly 55 percent of the planet, an area
comparable on Earth to the distance from Los Angeles to New Delhi,
India. Scientists report that the radar mapping data is providing
significant new knowledge about the surface of Venus and its
atmosphere.
All of the areas mapped show widespread evidence of volcanism,
said Project Scientist Dr. Steve Saunders, along with evidence of
tectonics, the process that produces mountains.
"Venus and Earth are the only planets in our solar system that
have linear mountain belts," he said. But the mountains on Venus are
not deeply eroded by rainfall and running water as are the mountains
on Earth.
Magellan also confirmed the number of Venus impact craters that
scientists had expected to find, judging from their earlier Earth-
based radar data. The smallest impact craters seen so far on the
surface are about 3 miles in diameter, indicating the dense Venus
atmosphere has effectively shielded the surface from bombardment of
smaller asteroids and comets.
There also is evidence that the poisonous, thick atmosphere of
Venus was not formed recently, Saunders said. Surface images indicate
it may be from 400 million to 800 million years old or even older.
The Venus atmosphere is 90 times heavier than that of Earth and is
composed primarily of carbon dioxide with significant amounts of
sulfuric acid at upper levels.
- more -
- 2 -
Saunders said scientists see in the images that linear mountain
belts are being pulled apart by gravitational forces on the planet.
New styles of volcanism have been found and lava channels
hundreds of miles long occur at several places on the plains.
Although lava channels have been found on Earth, none are as long or
as regular as those seen on Venus.
Another new type of volcanism is being referred to by scientists
as "pancake" domes. These structures appear to be up to 20 miles
across and nearly a mile high and form on the plains. Scientists
believe the domes are formed by an outflow of a pasty, thick lava,
similar to silicon-rich lavas on Earth. Volcanic domes also form on
Earth, but they are much smaller and form in volcanic calderas,
Saunders said.
The images also reveal indications of turbulent surface winds on
the planet. The evidence is in the form of wind streaks in the lee of
topographical obstacles, such as the small, low shield volcanoes on
the plains.
"Careful mapping of those wind streaks over the entire planet may
give us meteorological data about circulation of the atmosphere near
the surface," Saunders said.
To date, there have been 118 days of mapping and 973 orbits. A
total of 819.6 mapping orbits have been received on Earth, 45 percent
of the planet's surface, Project Manager Tony Spear said.
Fifteen days of mapping were lost, as expected, to superior
conjunction, the period last November when Earth and Venus were on
opposite sides of the sun and data transmission between the two
planets was impossible.
There have been other losses of data since mapping began last
Sept. 15, due to spacecraft problems and difficulties at the various
Deep Space Network stations, Spear said. But of the area covered by
mapping orbits, only 2.4 percent has been lost.
- end -
Photographs are available to media representatives to illustrate
this release by calling 202/453-8383.
Color: B&W:
90-HC-740 90-H-827
91-HC-47 91-H-47
90-H-782